Blue stain of wood - what is it and how to get rid of it?

The blue stain of wood, sometimes also called cyanosis, gives foresters and sawmill workers sleepless nights every year. Especially in spring and summer, wood easily changes color, darkens, and stains appear on its surface and structure, which significantly reduce the value of the wood material. What is this ailment and how to remove blue stain from wood?

What is wood stain?

Wood blue is the dark coloration of round coniferous wood and lumber. The spots that appear most often have a shade from blue through green to gray or black. Changes in the color of wood are caused by fungi from the ascomycete family and the so-called imperfect fungi, and more precisely their metabolites, i.e. metabolic products. The most common species of fungus is Ophiostoma , although there are more than 100 species of blue stain organisms.

Blue stain is transmitted, like all other fungi, by mycelial hyphae or wind-blown spores. Insects also unconsciously help with this. The disease primarily affects the sapwood of the wood, although sometimes it can also be found in the outer zone of the heartwood, which has not yet completely lignified. Infection develops most easily in spring and summer, when optimal atmospheric conditions (temperature and humidity) are created for mold growth. Therefore, first of all during this period it is necessary to observe the use of preventive measures.

Blue stain is divided into:

• exposed and hidden - if the criterion is the visibility of spots,
• raw and lumber – when the decisive factor is the type of infected material.

Some representatives of science additionally divide raw blue stain into: deadwood, burnt and storage blue.

How is wood blue stain formed?

If the tree is healthy and the bark is undamaged, cyanosis will most likely not develop. However, fungi that cause infection penetrate the trunk structure through the surface of the face, places where branches are cut off and damage to the bark, which occurs, for example, during the transport of logs and logs. From a financial point of view, the most dangerous for sawmills is cyanosis, which gets inside the tree through damaged bark. Most often, employees will detect it only after cutting the log into logs.

How does the blue stain of wood affect the properties of the raw material?

Blue stain infection causes very little change in the structure of the wood itself. It does not reduce its functional properties, and the raw material is still suitable for use in construction and as structural elements. What is of great importance to investors, however, are often the aesthetic properties and commercial value. Traces of blue stain may indicate that the wood was stored in inappropriate conditions or was poorly preserved. Mold symptoms suggest that the material has also been attacked by other fungi or microbes that cannot be seen with the naked eye.

How to prevent blue stain on the boards?

According to the principle that prevention is better than cure, it is worth ensuring that the blue stain of the wood does not appear at all. In the case of a standing tree stand, unfortunately, there are not many possibilities for action. The poor condition of forests in Poland is influenced by many factors. First of all, planning skidding under buildings (and not taking into account the quality of trees) and emphasizing the non-productive functions of forest areas give cyanobacteria a lot of time to develop.

Much more can be done when blue stain appears on the raw material or lumber. First of all, the period of wood storage in the spring and summer period should be limited to a minimum (and it is best to perform fellings only at the customer's request). It is also worth taking care of the protection of the collected material.

Fungicides that inhibit the growth of mycelium will be useful. Wood can also be stored in special polytunnels in conjunction with the use of chemicals or water sprinklers that create a humid microclimate, unfavorable for the development of fungi. But first of all, you should pay attention to the outer coating of the wood material. The less damage is done to the bark, the less chance the spores will have to develop.

Wood blue stain removal

How to get rid of wood stain? In the case of surface blue stain, it is enough to remove the infected piece of wood, e.g. by grinding or planing the layer or by other mechanical treatment. However, when there is a blue stain that got inside the wood or there is no possibility to use mechanical methods, it becomes necessary to use specialized chemicals.

Blue wood is treated with bleaching substances, such as:

• sodium compounds,
• calcium chlorides,
• oxalates.

The action of chemical compounds causes the gradual degradation of the mycelium, and finally its oxidation. Thanks to this, the wood regains its natural color. However, you must remember to clean the surface of chemicals with neutralizing agents after bleaching the wood.

It is assumed that the use of bleaching agents should not cause changes in the structure of wood, reduce its strength or damage the wood material. Before applying another protective layer (e.g. varnish or stain), it is worth checking whether there are any changes on the surface of the wood material.

The emergence and excessive development of wood cyanosis can mean huge losses in business and the loss of existing customers. Therefore, it is worth ensuring that blue stain does not form, and if it has already occurred, remove it as soon as possible. The necessary bleaching compounds sold by chemical wholesalers allow you to quickly and effectively get rid of wood infection.